Explosive composition



3,026,221 EXPLOSTVE (IQ-MPQEHTTQN William E. Kirst, Woodhury, N..l.,assignor to E. l. (in Pont de Nemours and Company, Wilmington, Deh, acorporation of Delaware Mo Drawing. Filed .lnly 21, 1958, Ser. No.749,632 2 Claims. (Cl. 149-39) The present invention relates to a novelblasting composition which is of high density. More particularly, the

present invention relates to a high-density blasting com- 7 positioncomprising low-cost ingredients.

In blasting operations, for example quarrying and stripping, the use ofa high-density explosive composition is highly desirable on atheoretical basis. High-density compositions providing greater weight ofexplosive, and thus increased available energy, per unit volume make possible the use of fewer and/ or smaller diameter boreholes, equivalentblasting energy being provided by a lesser volume of high-densityexplosive. The savings in drilling costs resulting from reduction innumber and size of the boreholes are of obvious importance. However, inpractice, these theoretical considerations are complicated by severalfactors.

In the main, the relatively high costs of the available high-densityexplosives, e.g. blasting gelatin, more than counteract the economieseffected by reduction in drilling costs. This factor, and also theundesirably high initiation sensitivity of blasting gelatin and thelike, has led to widespread usage in blasting operations of thelowercost but low-density ammonium nitrate-type compositions.

To overcome the aforementioned deficiencies of the high-densityexplosives, certain cast explosives which are of high density, low cost,and satisfactory sensitivity have been developed for use in blastingoperations. These cast compositions, in spite of their many advantages,are at times deficient in that their rigid nature prevents theirexpansion to fill the borehole volume, which naturally reduces theadvantages resulting from their high density. This problem is alsoencountered to some extent with the high-density blasting gelatins whichmust be tamped to fill the borehole space. Really efiicient tamping isseldom achieved, especially in those boreholes formed by the 4 jettingtechnique and thus having very irregular contours. Inasmuch as thejetting method of drilling is becoming more and more prevalent, thetamping procedure, on a whole, is becoming less and less popular.

Accordingly, an object of the present invention is the such a blastingcomposition which is free flowing in nature and can be readily poured tofill the entire volume of the borehole.

i have found that the foregoing objects may be achieved when I provide ablasting composition comprising sodium nitrate admixed withhigh-density, essentially spherical trinitrotoluene (TNT) pelletsrelatively uniform in size. In accordance with the present invention, ametallic fuel, which influences density and detonation velocity, and/ora hydrocarbon oil, which assists in maintaining the proper interminglingof ingredients, optionally may be included in the formulation.

The following examples serve to illustrate specific embodiments andfeatures of the present invention. However, they will be understood tobe illustrative only and not as limiting the invention in any manner.Parts in the examples are parts by weight, unless otherwise designated.The TNT pellets used in the exemplified experiments were a commerciallyavailable material termed pelletol comprising free-flowingwater-resistant pellets of TNT substantially spherical in form.

Example 1 Into a mixer of the type conventionally used in thepreparation of explosive compositions were charged 4000 parts of the TNTpellets and 6000 parts of sodium nitrate of a commercial grade havingthe following fineness specifications.

Tyler standard screens:

On 10 mesh 2.0% max. On 20 mesh 14.0% max. Through 100 mesh 15-40%.

The ingredients were mixed until a uniform blend was apparent and thenthe free-running mixture was discharged from the mixer. A4-inch-diameter, 24-inch-long metal can of the type conventionally usedfor explosives was packed with the formulation in the amount of about6725 parts. The density of the material within the can was 1.43 gramsper cubic centimeter. The explosive cartridge was submerged in water andwas initiated by a standard 4-pound pentolite (TNT-PETN) primer. Thecharge detonated at a velocity of 3135 meters per sec- Example 2 Aformulation comprising 36% by weight of the TNT pellets, 54% by weightof the sodium nitrate, and 10% by weight of ferrosilicon was preparedand packaged in accordance with the procedures of Example 1. Thefreerunning explosive, which was present in the metal container in theamount of 6880 parts, had a density, as packed, of 1.46 grams per cubiccentimeter. Upon initiation under water by the pentolite primer, thecharge detonated at a velocity of 3580 meters per second.

Example 3 Another mixing was prepared and packaged by the Example 1procedures, the composition comprising a free-running mixture of 38% ofthe TNT pellets, 60% of the sodium nitrate, and 2.0% of motor oil. Thefilled metal container held 6330 parts of the formulation which had adensity, as packed, of 1.36 gram per cubic centimeter. The charge wasinitiated under water by the pentolite primer and detonated at avelocity of 3970 meters per second.

Two other formulations were prepared, in one of which grained TNT wassubstituted for the pellets and in the other the TNT pellets werereplaced by flaked TNT. Formulation A consisted of 38.5% of grained TNT,60% of the sodium nitrate, and 1.5% of a low-viscosity mineral oil(commercially available as Bayol F), Formulation B being identical withthe exception that the TNT was flaked. The 4 x 24 inch metal containerheld only 5780 parts of Formulation A (density, 1.22 g./cc.) and only6020 parts of Formulation B (density, 1.27 g./cc.). When initiated bythe pentolite primer, Formulations A and B detonated at velocities of4100 and 3100 meters per second, respectively.

Example 4 A number of other free-running mixings were prepared andpackaged as aforedescribed, the compositions and the properties of themixings being summarized in the following table. In all cases, the mixeswere initiated under water by 4-pound pentolite primers.

Ingredients (wt. percent) Wt. of D. of Velocity of Mix N0. Metal FuelCompn. Compn. Detonation Bayol in car- (g./cc.) (KL/S90.) 'lNl NaNO Foil tridge Al FeSi Fe (parts) powder powder 1 Prilled sodium nitrate(coarse granules).

As has been exemplified, free-running explosive compositions ofhigh-density and desirable sensitivity may be readily prepared by simplemechanical admixture of TNT pellets with sodium nitrate and optionalmodifiers. Although the other ingredients naturally exert an influenceupon density, it may be seen from Example 3 that all other things beingequal, the use of pelletized TNT results in greater density than doesthe employment of either grained or flaked TNT. To facilitate theattainment of high density, the TNT pellets should be of high density.To expedite the formation of a uniform mixture, the TNT pellets shouldbe substantially spherical in form and relatively uniform in size, thatis, their diameter should fall within the limits of narrow range. Thus,the use of TNT pellets meeting the afore-mentioned prerequisitesconstitutes a critical feature of the present invention. Suitable TNTpellets are readily available commercially as pelletol pelleted TNT.These pelletol pellets are free-flowing and water-resistant. Thediameter of the individual pellets is inch. Their absolute density is1.55- 1.60 grams per cubic centimeter, while their bulk density fallswithin the range of O.901.05 grams per cubic centimeter. Although theseexemplified pellets function very satisfactorily and, thus, their useconstitutes a preferred embodiment of the present invention, other TNTpellets meeting the afore-mentioned requirements may be substituted,when available, for the exemplified material.

The TNT pellets are incorporated in the mixture in the amount of atleast 25% by weight, in order to insure propagation of the detonation.The most important factor determining the upper limit on the proportionof TNT used is an economic factor, the cost of the finished compositionbeing directly proportional, on the whole, to the amount of TNT present.Inasmuch as increases in the TNT content beyond 40% increase the totalcost of the composition without effecting material gains in itsperformance, I prefer to employ not more than 40% of TNT pellets in thecomposition.

To obtain the desired high density, the TNT pellets must be mixed withsodium nitrate as the oxidant, other conventional oxidants, for exampleammonium nitrate, being of too low absolute density to serve thepurposes of the present invention. The sodium nitrate is used in theamount of 4864%. Its granulation per se is not critical, althoughnaturally the finer granula-tions give higher packed densities thanthose resulting from the employment of very coarse sodium nitrate, forexample prills.

As illustrated in the foregoing examples, the novel blasting agentcompositions of the present invention are characterized by a bulkdensity of at least about 1.4 grams per cubic centimeter.

A metallic fuel optionally may be included in the formulation in anamount of up to about 20% by Weight. The inclusion of such fuelnaturally modifies density, oxygen balance, and velocity of detonation,and, thus, these factors must be considered in the selection of thespecific metallic fuel and its percentage. The metallic fuel naturallyshould be employed in finely divided state to provide an essentiallyuniform commingling of ingredients.

In addition to the exemplified ferrosilicon, aluminum, and iron,suitable metallic fuels include all those conventionally incorporatedinto blasting compositions, for example, manganese, magnesium,ferromanganese, and magnesiumsilicon alloys, among others.

The hydrocarbon oil, for example mineral oil or motor oil, may beincorporated, if desired, in slight amounts, e.g. up to 2%, as anantisegregating agent, that is to maintain the proper intermingling ofingredients.

Due to its free-running nature, the present explosive composition may beemployed in a number of ways in blasting operations. It may be packagedin conventional shells, say of paper, or in the Waterproof metal canscommonly used, the exemplified formulations being packaged in the lattermanner to facilitate testing. Advantageously, the composition may bepoured directly into dry boreholes to give an explosive columnconforming to the borehole contours. Wet holes may be provided with aliner of plastic, e.g. polyethylene, which prevents contact of thecomposition with water and permits the loading of the composition inloose form into wet holes. Of course, if the hygroscopic sodium nitrateis provided with a protective waterproof coating, the composition may beused in wet holes without the employment of auxiliary waterproofingmeans, e.g. the plastic borehole liner or metal or other Waterproofshells, because the other components of the formulation are notseriously affected by water.

The invention has been described in detail in the foregoing. However, itWill be apparent to those skilled in the art that many variations arepossible Without departure from the scope of the invention. I intend,therefore, to be limited only by the following claims.

I claim:

1. A substantially dry high-density, free-running explosive compositionwhich consists essentially of a heterogeneous mixture of 25-40% byweight of high-density TNT pellets relatively uniform in size andsubstantially spherical in form admixed with 4864% by weight of sodiumnitrate, 0-20% by Weight of a metallic fuel selected from the groupconsisting of ferrosilicon, aluminum, and iron, and 02% by weight of ahydrocarbon oil selected from the group consisting of motor oil andmineral oil, said explosive composition having a bulk density of atleast about 1.4 grams per cubic centimeter.

2. An explosive composition according to claim 7, wherein said TNTpellets have a diameter within the range of A A inch, a bulk density of0.90-1.05 grams per cubic centimeter, and an absolute density of1.55-1.60 grams per cubic centimeter.

References (Jilted in the file of this patent UNITED STATES PATENTS1,659,449 Snelling et al. 'Feb. 14, 1928 2,733,139 Winning Jan. 31, 19562,930,685 Cook et al. Mar. 29, 1960 FOREIGN PATENTS 755,695 GreatBritain Aug. 22, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,026 22l March 2O 1962..

William E. Kirst It is hereby certified that error appears in the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below.

Column 4, line 60, for the claim reference numeral "7" read l Signed andsealed this 24th day of July 1962.

(SEAL) Attest:

ERNEST w. SWIDER DAVID L. LADD Amsfing Officer Commissioner of Patents

1. A SUBSTANTIALLY DRY HIGH-DENSIYT, FREE-RUNNING EXPLOSIVE COMPOSITIONWHICH CONSISTS ESSENTIALLY OF A HETEROGENEOUS MIXTURES OF 25-40* BYWEIGHT OF HIGH-DENSITY TNT PELLETS RELATIVELY UNIFORM IN SIZE ANDSUBSTANTIALLY SPHERICAL IN FORM ADMIXED WITH 48-64% BY WEIGHT OF SODIUMNITRATE, 0-20% BY WEIGHT OF A METALLIC FUEL SELECTED FORM THE GROUPCONSISTING OF FERROSILICON, ALUMINUM, AND IRON, AND 0-2% BY WEIGHT OF AHYDROCARBON OIL SELECTED FROM THE GROUP CONSISTING OF MOTOR OIL ANDMINERAL OIL, SAID EXPLOSIVE COMPOSITION HAVING A BULK DENSITY OF ATLEAST ABOUT 1.4 GRAMS PER CUBIC CENTIMETER.